Abstract
Previous studies have shown that the inhibitory effect of betulinic acid (BA) on specificity protein 1 (Sp1) expression is involved in the prevention of cancer progression, but the mechanism of this effect remains to be delineated. In this study, we determined that BA treatment in HeLa cells increased the sumoylation of Sp1 by inhibiting sentrin-specific protease 1 expression. The subsequent recruitment of E3 ubiquitin-protein ligase RING finger protein 4 resulted in ubiquitin-mediated degradation in a 26S-proteosome-dependent pathway. In addition, both BA treatment and mithramycin A (MMA) treatment inhibited lung tumor growth and down-regulated Sp1 protein expression in Kras(G12D)-induced lung cancers of bitransgenic mice. In gene expression profiles of Kras(G12D)-induced lung cancers in bitransgenic mice with and without Sp1 inhibition, 542 genes were affected by MMA treatment. One of the gene products, cyclin A2, which was involved in the S and G(2)/M phase transition during cell cycle progression, was investigated in detail because its expression was regulated by Sp1. The down-regulation of cyclin A2 by BA treatment resulted in decreased retinoblastoma protein phosphorylation and cell cycle G(2)/M arrest. The BA-mediated cellular Sp1 degradation and antitumor effect were also confirmed in a xenograft mouse model by using H1299 cells. The knockdown of Sp1 in lung cancer cells attenuated the tumor-suppressive effect of BA. Taken together, the results of this study clarify the mechanism of BA-mediated Sp1 degradation and identify a pivotal role for Sp1 in the BA-induced repression of lung cancer growth.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adenocarcinoma / drug therapy*
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Adenocarcinoma / genetics
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Adenocarcinoma / metabolism*
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Adenocarcinoma / pathology
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Adenocarcinoma of Lung
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Animals
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Betulinic Acid
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Cell Cycle / drug effects
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Cell Cycle / genetics
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Cell Cycle Checkpoints / drug effects
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Cell Cycle Checkpoints / genetics
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Cell Line, Tumor
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Cell Proliferation / drug effects
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Cyclin A2 / genetics
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Cyclin A2 / metabolism
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Cysteine Endopeptidases
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Down-Regulation / drug effects
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Down-Regulation / genetics
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Endopeptidases / genetics
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Endopeptidases / metabolism
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Female
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HeLa Cells
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Humans
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Lung Neoplasms / drug therapy*
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Lung Neoplasms / genetics
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Lung Neoplasms / metabolism*
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Lung Neoplasms / pathology
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Mice
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Mice, Inbred BALB C
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Mice, Nude
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Mice, Transgenic
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Nuclear Proteins / genetics
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Nuclear Proteins / metabolism
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Pentacyclic Triterpenes
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Phosphorylation / drug effects
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Plicamycin / analogs & derivatives
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Plicamycin / pharmacology
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Proteasome Endopeptidase Complex / genetics
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Proteasome Endopeptidase Complex / metabolism
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Retinoblastoma Protein / genetics
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Retinoblastoma Protein / metabolism
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Sp1 Transcription Factor / antagonists & inhibitors*
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Sp1 Transcription Factor / genetics
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Sp1 Transcription Factor / metabolism*
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Sumoylation / drug effects*
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Sumoylation / genetics
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Transcription Factors / genetics
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Transcription Factors / metabolism
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Transcriptome / drug effects
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Transcriptome / genetics
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Triterpenes / pharmacology*
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Ubiquitin / genetics
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Ubiquitin / metabolism
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Ubiquitin-Protein Ligases / genetics
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Ubiquitin-Protein Ligases / metabolism
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Xenograft Model Antitumor Assays
Substances
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CCNA2 protein, human
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Cyclin A2
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Nuclear Proteins
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Pentacyclic Triterpenes
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RNF4 protein, human
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Retinoblastoma Protein
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Sp1 Transcription Factor
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Transcription Factors
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Triterpenes
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Ubiquitin
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mithramycin A
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Ubiquitin-Protein Ligases
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Endopeptidases
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SENP1 protein, human
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex
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ATP dependent 26S protease
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Plicamycin
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Betulinic Acid